Search for excited leptons in pp collisions at s = 7 TeV
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Citation
Chatrchyan, S., V. Khachatryan, A.M. Sirunyan, A. Tumasyan,
W. Adam, E. Aguilo, T. Bergauer, et al. “Search for Excited
Leptons in Pp Collisions at s = 7 TeV.” Physics Letters B 720, no.
4–5 (March 2013): 309–329. © CERN for the benefit of the CMS
Collaboration
As Published
http://dx.doi.org/10.1016/j.physletb.2013.02.031
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Elsevier
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Final published version
Accessed
Fri May 27 14:14:30 EDT 2016
Citable Link
http://hdl.handle.net/1721.1/90425
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Physics Letters B 720 (2013) 309–329
Contents lists available at SciVerse ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Search for excited leptons in pp collisions at
√
s = 7 TeV ✩
.CMS Collaboration CERN, Switzerland
a r t i c l e
i n f o
Article history:
Received 6 October 2012
Received in revised form 12 February 2013
Accepted 13 February 2013
Available online 19 February 2013
Editor: M. Doser
Keywords:
CMS
Physics
a b s t r a c t
Results are presented of a search for compositeness
in electrons and muons using a data sample of
√
pp collisions at a center-of-mass energy s = 7 TeV collected with the CMS detector at the LHC and
−1
corresponding to an integrated luminosity of 5.0 fb . Excited leptons (∗ ) are assumed to be produced
via contact interactions in conjunction with a standard model lepton and to decay via ∗ → γ , yielding a
final state with two energetic leptons and a photon. The number of events observed in data is consistent
with that expected from the standard model. The 95% confidence upper limits for the cross section for
the production and decay of excited electrons (muons), with masses ranging from 0.6 to 2 TeV, are 1.48
to 1.24 fb (1.31 to 1.11 fb). Excited leptons with masses below 1.9 TeV are excluded for the case where
the contact interaction scale equals the excited lepton mass. The limits on the cross sections are the most
stringent ones published to date.
© 2013 CERN. Published by Elsevier B.V. All rights reserved.
1. Introduction
The standard model (SM) of particle physics, albeit very successful, provides no explanation for the three generation structure
of the fermion families. Attempts to explain the observed hierarchy have led to a family of models postulating that quarks and
leptons might be composite objects of fundamental constituents
[1–9]. The fundamental constituents are bound by an asymptotically free gauge interaction that becomes strong at a characteristic
scale Λ. Compositeness models predict the existence of excited
states of quarks (q∗ ) and leptons (∗ ) at this characteristic scale of
the new binding interaction. Since these excited fermions couple to
the ordinary SM fermions, they can be produced via contact interactions in collider experiments and subsequently decay radiatively
to ordinary fermions through the emission of a W/Z/γ boson or via
contact interactions to other fermions. The excited leptons can also
be produced via gauge-mediated interactions, but the cross sections for these are negligible for the range of parameters that are
probed in this search and therefore this production mechanism is
not considered. The effective Lagrangian describing the interaction
of excited fermions [7] is parametrized by the scale Λ. Additionally, for decay via gauge mediated interaction, two factors f and f represent the relative strength of the coupling between the excited
fermions and isovector and isoscalar gauge fields, respectively. In
this Letter the convention f = f = 1 is adopted. The results for
✩
© CERN for the benefit of the CMS Collaboration.
E-mail address: cms-publication-committee-chair@cern.ch.
0370-2693/ © 2013 CERN. Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.physletb.2013.02.031
arbitrary f = f > 0 can be simply obtained by a rescaling of the
scale Λ to Λ/ f .
Searches at LEP [10–13], HERA [14], and the Tevatron [15–18]
found no evidence for excited leptons. At the Large Hadron Collider
(LHC) [19] at CERN, previous searches performed by the CMS [20]
and the ATLAS Collaborations [21] have also shown
√ no evidence
for excited leptons. At a center-of-mass energy of s = 7 TeV, with
36 pb−1 of data [20], CMS has excluded cross sections for the production and decay of the ∗ → γ channels higher than 0.16 to
0.21 pb (0.14 to 0.19 pb) in the e∗ (μ∗ ) channel for excited lepton masses ranging from 0.2 TeV to 2 TeV. In the same channels
and with more integrated luminosity, ATLAS excluded cross sections higher than 2.3 (4.5) fb for excited electrons (muons) masses
above 0.9 TeV, and excluded e∗ (μ∗ ) with masses M ∗ below
1.87 (1.75) TeV for the scale of contact interaction Λ = M ∗ [21].
This Letter presents a search for excited leptons, e∗ and μ∗ ,
using
a data sample of pp collisions at a center-of-mass energy
√
s = 7 TeV collected with the CMS detector at the LHC in 2011
and corresponding to an integrated luminosity of 5.0 ± 0.1 fb−1 .
The production of an excited lepton in association with an oppositely charged lepton of the same flavor, via four-fermion contact
interactions, is considered. Thus when the excited lepton decays
via ∗ → γ , there are two oppositely charged leptons and a photon in the final state.
2. The CMS detector
The central feature of the Compact Muon Solenoid (CMS) detector is a superconducting solenoid, of 6 m internal diameter and
310
CMS Collaboration / Physics Letters B 720 (2013) 309–329
12.5 m in length, which provides an axial field of 3.8 T. Starting
from the collision point, the first three detector components inside
the solenoid are the silicon pixel and strip trackers; the lead–
tungstate crystal electromagnetic calorimeter (ECAL), comprising
a central (barrel) section and two forward (endcap) sections; and
the brass/scintillator hadron calorimeter (HCAL). Extensive forward
calorimetry complements the coverage provided by the barrel and
endcap detectors. The tracker consists of 10 layers of silicon strip
detectors in addition to the pixel detectors. Four stations of muon
detectors are embedded in the steel yoke of the superconducting solenoid, including forward sections in order to extend the
covered pseudorapidity region up to |η| < 2.4. The pseudorapidity (η ) is defined as η = − ln[tan(θ/2)]. The CMS detector uses a
right-handed coordinate system, with the origin at the nominal interaction point, the x axis pointing to the center of the LHC, the
y axis pointing up (perpendicular to the LHC plane), and the z
axis along the anticlockwise-beam direction. The polar angle θ is
measured from the positive z axis and the azimuthal angle φ is
measured in the x– y plane. The projection of the momentum on
to the x– y plane is used to define the transverse momentum p T
and the transverse energy E T . The details of the CMS detector are
described elsewhere [22].
3. Signal and background
The dominant, irreducible SM background in this search is
Drell–Yan production of + − γ where the final state photon is
either radiated by an initial-state parton (initial-state radiation,
ISR), or originates from one of the final-state leptons (final-state
radiation, FSR). The second-most important background is due to
Drell–Yan production associated with jets (Z + jets), where a jet is
misidentified as a photon (see Section 5). Another important background in the e∗ channel is due to W + jets events with an FSR or
ISR photon where a jet is misidentified as an electron. In the μ∗
channel, backgrounds from these W + jets processes that lead to
one true, one misidentified muon, and a true photon in the final
state have been estimated to be negligible. Other less significant
backgrounds originate from diboson events (WW, WZ, ZZ, W + γ ),
tt production, and, for the electron channel, γ γ production. These
backgrounds are mainly suppressed by requiring high transverse
momentum thresholds on the leptons and photon. Backgrounds
arising from misidentified photons or misidentified electrons are
estimated using a data-driven technique which is described in Section 5. The other backgrounds are estimated from the simulation.
Signal samples in both electron and muon channels are produced using pythia (pythia 6.424 [23] and pythia 8.145 [24] respectively) based on the leading order (LO) compositeness model
described in Ref. [7]. The signal cross sections are calculated with
pythia 6.424, corrected to include the branching ratio for the 3body decays via contact interaction as per Ref. [7] which is not
implemented in pythia, with the Q 2 scale set to the square of the
mass of the excited lepton (M 2∗ ).
Samples are obtained for different values of the excited lepton mass and Λ = 4 TeV, with the CTEQ6L1 [25] parametrization
for the parton distribution functions. This particular choice of the
value of Λ has no impact on the simulated kinematics and all results are presented independently of the value of Λ, except for
the signal yield in Fig. 1 and Fig. 2. The SM background samples: Z + γ , W + γ , tt, Z + jets, W + jets, and WW are generated
with MadGraph 4.5.1 [26]. pythia has been used to perform the
fragmentation and hadronization of samples generated with MadGraph. The diboson samples (WZ, ZZ) are generated using pythia
6.424. The main background Z + γ has been generated to correspond to an integrated luminosity of around 7 fb−1 . For all these
SM background processes, the cross sections are scaled to the
max
Fig. 1. The distribution of events as a function of M min
γ (top) and M γ (bottom), expected in the presence of an excited electron with a mass of 0.2 TeV. The red dotted
histogram corresponds to the contribution from the standard model backgrounds
containing two real electrons and a real photon. The blue slanting hatched (green
horizontal hatched) histograms correspond to the contribution from misidentified
photon (electrons). The black solid circles correspond to the observed data. The red
solid line histogram corresponds to the signal distribution for a mass of 0.2 TeV. The
dark grey double hatched region shows the uncertainty in the SM expectation. (For
interpretation of the references to color in this figure legend, the reader is referred
to the web version of this Letter.)
next-to-leading order (NLO) cross sections obtained from the parton level integrator mcfm [27]. For the main background Z + γ , the
theoretical scale uncertainty has been evaluated using mcfm to be
+2.4%, −1.6%. All Monte Carlo events used in this analysis have
been passed through the detailed simulation of the CMS detector
based on Geant4 [28].
4. Event reconstruction and selection
Candidate events for the electron (muon) channel are selected
using triggers with the lowest possible thresholds on lepton transverse momentum. This corresponds to a transverse momentum
threshold of 33 (24) GeV for the initial periods and 33 (40) GeV
for the later periods of data collection in the electron (muon)
channel. The trigger thresholds were raised in response to the increased mean instantaneous luminosity. For the leptons selected in
the analysis, the trigger efficiencies are 100% (97%) in the electron
(muon) channel. The two leptons and the photon in signal events
are expected to be isolated from other particles in the event. This
CMS Collaboration / Physics Letters B 720 (2013) 309–329
max
Fig. 2. Distribution of M min
γ and M γ for the excited electron analysis (top) and excited muon analysis (bottom). The black solid circles, the red squares and the green
open circles correspond to the observed data, the background distribution and the
signal distribution, respectively. The optimized selection boundaries are shown for
an excited lepton mass of 0.2 TeV. The sample is normalized to 5 fb−1 of integrated
luminosity. (For interpretation of the references to color in this figure legend, the
reader is referred to the web version of this Letter.)
can be quantified by isolation variables, obtained by summing the
energy deposits present inside a geometrical cone around the particle, in the tracker or in the calorimeters. Events with at least
one well-reconstructed primary vertex, one isolated high-p T photon, and two isolated high-p T leptons are used in this analysis.
Electron identification is performed using clusters of localized
energy deposits in the ECAL. An energy deposit in the ECAL due
to an electron is identified by imposing requirements on shower
shapes of the ECAL clusters and isolation variables as well as
the ratio of the energies deposited in the hadron and electromagnetic calorimeters (H / E). A reconstructed track correctly associated with an ECAL cluster is also required. For the electron
channel, the electrons are required to have a transverse energy
E T > 35 (40) GeV in the ECAL barrel (endcap) and |η| < 2.5, excluding the transition region 1.4442 < |η| < 1.560 between the
ECAL barrel and endcap regions. The electron is required to be isolated both
in the tracker and calorimeter within a cone of radius
R ≡ (φ)2 + (η)2 < 0.3 around its direction. In the tracker,
the scalar sum of the p T of the tracks, that are at least 0.7 GeV
311
in p T and lie outside a cone of radius R = 0.04 relative to the
electron, is required to be less than 5 GeV. For the isolation using
the calorimeters, a variable E Tiso is introduced, defined as the total
sum of transverse energy deposits excluding deposits associated
with the electron. In the barrel, E Tiso is required to be less than
0.03E T + 2.0 GeV, and in the endcap: for E T < 50 GeV, the total
E Tiso is required to be below 2.5 GeV; for E T > 50 GeV, it is required to be below 0.03E T + 1.0 GeV.
For photons, identification criteria on the shower shapes, isolation variables and H / E are applied to energy clusters in the
ECAL [29]. Photon candidates are required to have clusters with
E T > 35 GeV and to be in the central region (barrel) of the ECAL
with |η| < 1.4442. The photon is also required to be isolated
within a cone of radius R < 0.4 around its direction, both in the
tracker and calorimeter. The cone axis is taken to be the direction of the line joining the barycenter of the energy cluster to the
primary vertex. In the tracker, the scalar sum of the transverse momenta of the tracks, excluding tracks within an inner cone of 0.04,
is required to be less than 0.001p T + 2 GeV. In the ECAL, the total
E Tiso in the barrel, excluding deposits associated with the photon,
is required to be below 0.006E T + 4.2 GeV, whereas for the HCAL
isolation, it is required to be below 0.0025E T + 2.2 GeV.
Muons are reconstructed by combining tracks from the inner
tracker and the outer muon system, requiring at least one hit in
the pixel tracker, hits in more than 8 tracker layers and track
segments reconstructed in at least two muon stations. Since the
segments have multiple hits that typically occur in different muon
detectors and are therefore separated by thick layers of iron, the
latter requirement significantly reduces the probability of a hadron
being misidentified as a muon. For the muon channel, two muons
are required with each having |η| < 2.1; and the higher (lower)
momentum muon must have p T > 45 (40) GeV. In order to reduce
the cosmic-rays muon background, the transverse impact parameters of both muon tracks with respect to the primary vertex of
the event are required to be less than 0.2 cm and muon pairs that
are back-to-back in the transverse plane are rejected, with the angle between two muon tracks below π − 0.02. Furthermore, the
muon is required to be isolated such that the scalar sum of the
transverse momenta of all tracks originating at the interaction vertex, excluding the muon itself, within a R < 0.3 cone around its
direction is less than 10% of its p T .
In order to reject Drell–Yan events with final state radiation, the
distance in (η , φ ) coordinates between the photon and the leading
lepton, R (, γ ) is required to be R (, γ ) > 0.5 for = e and
R (, γ ) > 0.7 for = μ. Two lepton–photon invariant masses
can also be computed, because the final state is composed of two
leptons and one photon. For the electron channel, the dielectron
invariant mass is required to be above 60 GeV and each of the
dielectron and electron–photon invariant masses are required to
be outside a ±25 GeV window centered at the nominal Z mass
(91.19 GeV). For the muon channel, the dilepton invariant mass is
required to be 25 GeV above the nominal Z mass. Fig. 1 shows
max
the distribution of M min
γ and M γ , the lower and higher invariant
mass respectively. In the case of a signal, the correct assignment
max
peaks at the excited lepton mass. In the M min
γ –M γ plane, the signal is distributed along two mutually perpendicular narrow bands.
This shape determines the final selection cuts as outlined below
and is illustrated in Fig. 2 for M ∗ = 0.2 TeV. Identical boundaries
are used for the electron and muon channel. The only difference
in the selection between the two channels is the Z veto, which, in
the electron channel, is also applied on electron–photon invariant
mass.
The background is located in the low invariant mass region,
while the signal populates the higher invariant mass region. Using simulations, the boundaries of the signal region for a given
312
CMS Collaboration / Physics Letters B 720 (2013) 309–329
Table 1
Measured signal and expected background event numbers for the electron and muon channels as a function of the mass of the excited lepton. The signal efficiency with its
corresponding uncertainty is given as signal . The expected numbers of background events are reported as N bkgd with Clopper–Pearson errors [30] along with the observed
max
data N data . The boundary values for M min
γ and M γ , which correspond to the signal region, are also given. The signal efficiencies shown with † symbol are obtained from a
polynomial curve fitted to the signal efficiencies for the mass points that have been simulated.
M ∗
(TeV)
M min
γ
M max
γ
Electron channel
(TeV)
(TeV)
signal (%)
N bkgd
N data
signal (%)
N bkgd
N data
0.2
0.19–0.21
0.20–0.21
24.8 ± 1.8
1.1
1.0+
−0.5
2
28.2 ± 1.3
1.7
1.2+
−0.6
2
0.3
0.23–0.37
0.29–0.31
30.0 ± 2.2†
1
34.4 ± 1.6†
1
39.1 ± 1.8
1
42.1 ± 1.9†
0
45.4 ± 2.0
0
45.9 ± 2.1†
0
45.3 ± 2.0
0
48.5 ± 2.1
0
50.0 ± 2.2
0
50.8 ± 2.2
0
50.4 ± 2.2
0.4
0.28–0.52
0.38–0.41
32.7 ± 2.4
0.5
0.35–0.65
0.47–0.53
34.8 ± 2.6†
0.6
0.42–0.78
0.55–0.64
36.6 ± 2.6
0.7
0.49–0.91
0.65–0.76
37.8 ± 2.7†
0.8
0.56–1.04
0.75–0.88
37.8 ± 2.7
1.0
0.70–1.30
0.75–1.08
40.4 ± 2.8
1.2
0.84–1.56
0.75–1.34
41.1 ± 2.9
1.5
1.05–1.95
0.75–1.67
41.7 ± 2.9
2.0
1.40–2.60
0.75–2.23
43.5 ± 3.1
Muon channel
2.1
1.2+
−0.8
1.4
0.1 +
−0.1
+1.4
0.0−0.0
1.4
0 . 0+
−0.0
+1.4
0.1−0.0
1.4
0 . 0+
−0.0
1.4
0 . 0+
−0.0
1.4
0 . 0+
−0.0
+1.4
0.0−0.0
1.4
0 . 0+
−0.0
2.6
5.4+
−1.8
2.0
1.6+
−0.9
1.4
0.0+
−0.0
1.4
0.0+
−0.0
1.7
1.0+
−0.6
1.4
0.0+
−0.0
1.4
0.0+
−0.0
1.4
0.0+
−0.0
1.4
0.0+
−0.0
1.4
0.0+
−0.0
2
3
1
0
0
0
0
0
0
0
mass have been chosen to optimize the expected limit. The final
values for different excited lepton masses are shown in Table 1.
For M ∗ = 0.2 TeV, the horizontal band is small, in order to reduce the background contamination. For M ∗ = 0.4 TeV, a larger
horizontal band can be used, the increase of the background contamination being compensated by the gain in signal efficiency. For
higher excited lepton masses, the horizontal band is large to improve the signal efficiency in regions where almost no background
is present.
5. Background due to particle misidentification
Hadronic jets in which a π 0 carries a significant fraction of
the energy may be misidentified as isolated photons. Thus Z +
jets events are a potential background for this search. The photon misidentification rate is measured directly from a data sample
dominated by jets, with a photon-like candidate cluster embedded inside, which can potentially be misidentified as a photon.
The misidentification rate is defined as the ratio of the number
of photon candidates passing all the photon selection criteria (numerator) to the number of photon candidates that pass a loose set
of shower shape requirements but fail one of the photon isolation
criteria (denominator). The misidentification rate is estimated in
bins of photon E T . The numerator sample can have a contribution
from isolated true photons. This misidentification rate is therefore
corrected by using the probability distribution of energy-weighted
shower width (σηη ) of isolated true photons computed in units of
crystal size, which is different from that of non-isolated photons.
The true photon fraction in the numerator is estimated by fitting
these two different shower shapes to the shower shape distribution of the numerator sample, and subtracted from the numerator.
In order to estimate the contribution of misidentified photons in
the analysis, the misidentification rate is applied to a subsample
of data events containing one photon candidate and satisfying all
other selection criteria. This rate is calculated in photon E T bins of
(0.03–0.05, 0.05–0.075, 0.075–0.09, 0.09–0.2) TeV. Fig. 3 shows the
E T dependence of the photon misidentification rate. The calculated
misidentified photon rate is found to be 0.28, 0.07, 0.06 and 0.09
for the above mentioned E T bins.
From a fit, the measured rate is parametrized by a function,
f γmisid ( E T ), as given in Eq. (1) with a, b and c being the fit parameters:
f γmisid ( E T ) = a +
b
( E T )c
.
(1)
Fig. 3. The jet-to-photon misidentification rate as a function of E T . The dashed line
is the 40% uncertainty band.
An uncertainty of 40% is assigned to this function which envelopes the spread of data points relative to the fit. The jet to
photon misidentification is estimated by applying this misidentification rate to a sample passing all our selection requirements,
including triggers, except a requirement that the photon candidate
fails one of the photon identification criteria and passes instead the
loose identification requirements. Applied to the lowest mass point
of 0.2 TeV, the contribution of photon misidentification background
0.16
in the full selection is found to be 0.07+
−0.07 events for both the
electron and the muon channels. It is negligible for higher mass
points.
Backgrounds with zero or one real electron can contribute to
the e∗ search. The largest contributions come from processes such
as W(→ eν ) + jet + γ where the jet in the event is misidentified as an electron. Misidentification can occur when photons
coming from π 0 s inside a jet convert to an e+ e− pair and are
misidentified as electrons. Other possible sources include when
a charged particle within a jet provides both the track in the
tracker and an electromagnetic cluster that together fake an electron signature, or when a track from a charged particle matches
with a nearby energy deposition in the calorimeter from another
particle. The misidentification rate is calculated as the ratio between the number of candidates passing the electron selection
criteria with respect to those satisfying looser selection criteria.
CMS Collaboration / Physics Letters B 720 (2013) 309–329
Table 2
Details of the expected background compositions for several masses, showing contributions from Z + γ MC sample, misidentified γ and misidentified electron estimated from data. The uncertainties are reported as the quadratic sum of statistical
and systematic errors.
M ∗
(TeV)
Electron channel
Z + γ MC
Misid
0.2
1.1
0.8+
−0.5
0.4
0.6
Muon channel
Misid electron
Z + γ MC
Misid
0.16
0.07+
−0.07
0.17
0.08+
−0.07
1.7
1.0 +
−0.6
0.16
0.07 +
−0.07
1.4
0.0+
−0.0
0.16
0.07+
−0.07
0.02
0.01+
−0.01
1.9
1.6 +
−0.9
0.45
0.00 +
−0.00
1.4
0.0+
−0.0
0.45
0.00+
−0.00
0.08
0.00+
−0.00
1.4
0.0 +
−0.0
0.45
0.00 +
−0.00
γ
γ
The looser selection criteria require only that the first tracker layer
contributes a hit to the electron track and that offline emulations
of the online trigger requirements (“loose identification requirements”) on shower shape σηη and the ratio H / E are satisfied. This
misid
( E T , η ))
ratio is estimated as a function of E T in bins of η ( f electron
using a data sample selected with single-photon triggers [31]. The
jet to electron misidentified background in e∗ is estimated by applying this misidentification rate to a sample passing all our selection requirements, including triggers, except requiring one of
the electron candidates to fail the electron identification criteria
and pass instead the loose identification requirements. The systemmisid
atic uncertainty on f electron
( E T , η) is determined using a sample of
events containing two reconstructed electrons as in [31]. The contribution from jet events to the dielectron mass spectrum can be
determined either by applying the misidentification rate twice on
events with two loose electrons or by applying the misidentification rate once on events with one fully identified electron and one
loose electron. The first estimate lacks contributions from W + jets
and γ + jets events while the second estimate is contaminated
by Drell–Yan events. These effects are corrected using simulated
samples. If the misidentification rate method is correct, the two
corrected estimations should agree. Both estimates are found to
agree well and the residual difference of 40% between the two estimates is taken as the systematic uncertainty on the jet to electron
misidentification rate. The contribution from events which have
0.17
zero or one real electron is 0.08+
−0.07 for the lowest mass point
of 0.2 TeV and is negligible for higher mass points.
6. Results
After all selection steps the expected background for M ∗ >
1. 4
0.7 TeV is found to be 0+
−0.0 event in the simulated sample. The
signal efficiency increases with the mass of the excited lepton,
from 25% to 44% in the electron channel and 28% to 50% in the
muon channel. All numbers are summarized in Table 1. The expected numbers of signal events and irreducible background events
are evaluated from simulation while the contribution of misidentified particles is derived from data. The background composition
for several mass points, 0.2 TeV, 0.4 TeV and 0.6 TeV for both
channels is shown in Table 2. The uncertainties in the description
of the detector performance, such as lepton energy or momentum
resolution, lepton and photon energy scales, have been included in
the systematic uncertainties. The impact on the signal yield corresponds to an uncertainty of ±2% and ±3.5%, for the electron
and muon channels respectively. Effects caused by the increase in
the typical number of additional pp interactions (‘pileup’) per LHC
bunch crossing are modeled by adding to the generated events
multiple collisions with a multiplicity distribution matched to the
luminosity profile of the collision data. To evaluate the systematic uncertainty associated with the pileup simulation, the mean
of the distribution of the pileup interactions is varied by 5%, leading to a variation of 3.0% (0.6%) in the simulated backgrounds and
1.0% (1.5%) in signal yields in the electron (muon) channel. An
313
additional systematic uncertainty of 10% is assigned to the background to account for uncertainties associated with the choice of
parton distribution functions. The uncertainty in the luminosity
normalization is 2.2% [32].
As seen in Table 1, for masses above 0.5 TeV, no data events
pass the criteria designed to select excited lepton signatures. Using a single bin counting method, upper limits are provided on the
production cross section times branching fraction of excited electrons and excited muons at the 95% confidence level. The method
is implemented in the statistical package developed by the Higgs
study group [33]. The computation has been performed using both
a Bayesian [34,35] and a CLs [36,37] approach; the results are
found to be consistent with each other. The results presented here
are from the frequentist CLs approach, without the use of the
asymptotic approximation [33]. The background and signal uncertainties are dominated by completely uncorrelated uncertainties.
The integrated luminosity normalization uncertainty is considered
separately, with 100% correlation between signal and background.
The nuisance parameters related to the uncertainties on the background are treated according to gamma probability distribution
functions. The uncertainties on the signal yield and the integrated
luminosity normalization are taken into account via a lognormal
treatment of nuisance parameters. The observed limits for the electron and the muon channels are shown in Fig. 4. Production cross
sections higher than 1.48 to 1.24 fb (1.31 to 1.11 fb) are excluded
at the 95% confidence limit (CL) for e∗ (μ∗ ) masses ranging from
0.6 to 2 TeV. The structure observed in the expected and observed
limits results from the limited sizes of the simulated background
samples. The optimization of the invariant masses selecting the
max
M min
γ –M γ signal region has been determined from simulation
of signal reference mass points, ranging from M ∗ = 0.2 TeV to
2.0 TeV in steps of 0.2 TeV. For lower masses, the selected signal
regions do not overlap. For continuous coverage, additional mass
points for M ∗ < 0.6 TeV have been added by interpolating the cut
thresholds and the signal efficiencies. Limits for masses between
0.2 and 0.4 TeV are less stringent because of the presence of background in this region.
In the excited muon channel, as visible in Table 1, the bump
at M μ∗ ∼ 0.5 TeV corresponds to a region where the background
1. 4
is found to be 0.0+
−0.0 in the simulated sample while one data
event is observed. Also in this channel, the shape of the uncertainty bands at M μ∗ = 0.7 TeV corresponds to a region where the
1. 7
background is found to be 1.0+
−0.6 in the simulated sample while
zero data events are observed. For high excited lepton masses, the
muon channel cross section limit is slightly lower than the electron channel limit because of the difference in the acceptance. For
lower excited lepton masses, the sensitivity of the electron channel
is also reduced because of misidentification of photons and electrons.
The set of Λ–M ∗ values for which the theoretical cross section times branching fraction is higher than the 95% upper limit
on cross section, is considered as excluded region of the parameter space. The exclusion region in the Λ–M ∗ plane is shown in
Fig. 5. The displayed uncertainty band corresponds to the uncertainty on the cross section limits, and does not take into account
uncertainties on the theoretical signal cross section. The region is
theoretically excluded, where M ∗ > Λ. The signal cross sections
are estimated with the Q 2 scale set to the square of the mass of
excited lepton (M 2∗ ). If the Q 2 scale is varied to M 2∗ /2, the limit
for Λ = M ∗ increases by 1.5% and if it is varied to 2M 2∗ , the limit
for Λ = M ∗ decreases by 2.4%. The impact of the parton distribution functions (PDF) uncertainties on the signal is smaller than 1%.
Assuming the same masses for e∗ and μ∗ , the two counting experiments have been combined using the CLs approach, improving
the excluded cross section limit to 0.73 to 0.60 fb for masses from
314
CMS Collaboration / Physics Letters B 720 (2013) 309–329
Fig. 4. Expected and observed 95% CL upper limits on the cross section of the studied channel for the different excited electron (top) and muon (bottom) mass points,
using the CLs method. The excluded region is above the curve. The black solid lines
correspond to the excited lepton LO cross sections times branching ratio for different Λ scales. The one (two) standard deviation uncertainty bands are shown in
green (yellow). (For interpretation of the references to color in this figure legend,
the reader is referred to the web version of this Letter.)
0.6 to 2 TeV. Allowing e∗ and μ∗ to have different masses, the excluded cross sections would also be within this range. The following uncertainties have been considered as completely correlated
between the two channels: the photon scale factor uncertainties in
signal and background, the photon misidentification rate systematic uncertainty not related to statistics, the luminosity uncertainty,
the pileup simulation uncertainty, the Z + γ normalization uncertainty, and the Z + γ PDF uncertainty. The other uncertainties are
considered as 100% uncorrelated.
7. Summary
A search has been performed with the CMS detector for excited leptons in the electron (pp → ee∗ → eeγ ) and muon (pp →
μμ∗ → μμγ ) channels. For each excited lepton mass, the excluded cross section can be associated with a value for the new
interaction scale Λ. Excited leptons (electrons or muons) with
masses below 1.9 TeV are excluded for the scale of contact interaction Λ = M ∗ . Production cross sections higher than 1.48 to
Fig. 5. Expected and observed 95% CL lower limits on the Λ scale for the different excited electron (top) and muon (bottom) mass points, using the CLs method.
The excluded region is below the curve. These limits are computed with the LO
signal cross section obtained from pythia 6.424. The one standard deviation uncertainty band is shown in green. The bands do not include the uncertainty on signal
cross section. The grey area corresponds to the theoretically excluded region where
M ∗ > Λ. (For interpretation of the references to color in this figure legend, the
reader is referred to the web version of this Letter.)
1.24 fb (1.31 to 1.11 fb) are excluded at the 95% CL for e∗ (μ∗ )
masses ranging from 0.6 to 2 TeV. The slightly better sensitivity in
the muon channel is due to its better acceptance and efficiency,
and also, for lower ∗ masses, to the fact that there is a higher
background in the electron channel arising from particle misidentification. These limits are the most stringent published to date.
Acknowledgements
We congratulate our colleagues in the CERN accelerator departments for the excellent performance of the LHC machine. We thank
the technical and administrative staff at CERN and other CMS
institutes, and acknowledge support from: FMSR (Austria); FNRS
and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil);
MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS
(Colombia); MSES (Croatia); RPF (Cyprus); MoER, SF0690030s09
and ERDF (Estonia); Academy of Finland, MEC, and HIP (Finland);
CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany);
GSRT (Greece); OTKA and NKTH (Hungary); DAE and DST (India);
CMS Collaboration / Physics Letters B 720 (2013) 309–329
I± (Iran); SFI (Ireland); INFN (Italy); NRF and WCU (Republic of
Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLP-FAI
(Mexico); MSI (New Zealand); PAEC (Pakistan); MSHE and NSC
(Poland); FCT (Portugal); JINR (Armenia, Belarus, Georgia, Ukraine,
Uzbekistan); MON, RosAtom, RAS and RFBR (Russia); MSTD (Serbia); MICINN and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC (Taipei); TUBITAK and TAEK (Turkey); STFC (United
Kingdom); DOE and NSF (USA). Individuals have received support from the Marie-Curie programme and the European Research
Council (European Union); the Leventis Foundation; the A.P. Sloan
Foundation; the Alexander von Humboldt Foundation; the Belgian
Federal Science Policy Office; the Fonds pour la Formation à la
Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium);
the Agentschap voor Innovatie door Wetenschap en Technologie
(IWT-Belgium); the Council of Scientific and Industrial Research,
India; and the HOMING PLUS programme of Foundation for Polish
Science, cofinanced from European Union, Regional Development
Fund.
Open access
This article is published Open Access at sciencedirect.com. It
is distributed under the terms of the Creative Commons Attribution License 3.0, which permits unrestricted use, distribution, and
reproduction in any medium, provided the original authors and
source are credited.
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CMS Collaboration
S. Chatrchyan, V. Khachatryan, A.M. Sirunyan, A. Tumasyan
Yerevan Physics Institute, Yerevan, Armenia
W. Adam, E. Aguilo, T. Bergauer, M. Dragicevic, J. Erö, C. Fabjan 1 , M. Friedl, R. Frühwirth 1 , V.M. Ghete,
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D. Liko, I. Mikulec, M. Pernicka † , B. Rahbaran, C. Rohringer, H. Rohringer, R. Schöfbeck, J. Strauss,
A. Taurok, W. Waltenberger, G. Walzel, E. Widl, C.-E. Wulz 1
Institut für Hochenergiephysik der OeAW, Wien, Austria
316
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V. Mossolov, N. Shumeiko, J. Suarez Gonzalez
National Centre for Particle and High Energy Physics, Minsk, Belarus
M. Bansal, S. Bansal, T. Cornelis, E.A. De Wolf, X. Janssen, S. Luyckx, L. Mucibello, S. Ochesanu, B. Roland,
R. Rougny, M. Selvaggi, Z. Staykova, H. Van Haevermaet, P. Van Mechelen, N. Van Remortel,
A. Van Spilbeeck
Universiteit Antwerpen, Antwerpen, Belgium
F. Blekman, S. Blyweert, J. D’Hondt, R. Gonzalez Suarez, A. Kalogeropoulos, M. Maes, A. Olbrechts,
W. Van Doninck, P. Van Mulders, G.P. Van Onsem, I. Villella
Vrije Universiteit Brussel, Brussel, Belgium
B. Clerbaux, G. De Lentdecker, V. Dero, A.P.R. Gay, T. Hreus, A. Léonard, P.E. Marage, A. Mohammadi,
T. Reis, L. Thomas, G. Vander Marcken, C. Vander Velde, P. Vanlaer, J. Wang
Université Libre de Bruxelles, Bruxelles, Belgium
V. Adler, K. Beernaert, A. Cimmino, S. Costantini, G. Garcia, M. Grunewald, B. Klein, J. Lellouch,
A. Marinov, J. Mccartin, A.A. Ocampo Rios, D. Ryckbosch, N. Strobbe, F. Thyssen, M. Tytgat,
P. Verwilligen, S. Walsh, E. Yazgan, N. Zaganidis
Ghent University, Ghent, Belgium
S. Basegmez, G. Bruno, R. Castello, L. Ceard, C. Delaere, T. du Pree, D. Favart, L. Forthomme,
A. Giammanco 2 , J. Hollar, V. Lemaitre, J. Liao, O. Militaru, C. Nuttens, D. Pagano, A. Pin, K. Piotrzkowski,
N. Schul, J.M. Vizan Garcia
Université Catholique de Louvain, Louvain-la-Neuve, Belgium
N. Beliy, T. Caebergs, E. Daubie, G.H. Hammad
Université de Mons, Mons, Belgium
G.A. Alves, M. Correa Martins Junior, D. De Jesus Damiao, T. Martins, M.E. Pol, M.H.G. Souza
Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro, Brazil
W.L. Aldá Júnior, W. Carvalho, A. Custódio, E.M. Da Costa, C. De Oliveira Martins, S. Fonseca De Souza,
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Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil
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Instituto de Fisica Teorica, Universidade Estadual Paulista, Sao Paulo, Brazil
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M. Vutova
Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria
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University of Sofia, Sofia, Bulgaria
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Universidad de Los Andes, Bogota, Colombia
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Technical University of Split, Split, Croatia
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University of Split, Split, Croatia
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Institute Rudjer Boskovic, Zagreb, Croatia
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University of Cyprus, Nicosia, Cyprus
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Charles University, Prague, Czech Republic
Y. Assran 7 , S. Elgammal 8 , A. Ellithi Kamel 9 , S. Khalil 8 , M.A. Mahmoud 10 , A. Radi 11,12
Academy of Scientific Research and Technology of the Arab Republic of Egypt, Egyptian Network of High Energy Physics, Cairo, Egypt
M. Kadastik, M. Müntel, M. Raidal, L. Rebane, A. Tiko
National Institute of Chemical Physics and Biophysics, Tallinn, Estonia
P. Eerola, G. Fedi, M. Voutilainen
Department of Physics, University of Helsinki, Helsinki, Finland
J. Härkönen, A. Heikkinen, V. Karimäki, R. Kinnunen, M.J. Kortelainen, T. Lampén, K. Lassila-Perini,
S. Lehti, T. Lindén, P. Luukka, T. Mäenpää, T. Peltola, E. Tuominen, J. Tuominiemi, E. Tuovinen, D. Ungaro,
L. Wendland
Helsinki Institute of Physics, Helsinki, Finland
K. Banzuzi, A. Karjalainen, A. Korpela, T. Tuuva
Lappeenranta University of Technology, Lappeenranta, Finland
M. Besancon, S. Choudhury, M. Dejardin, D. Denegri, B. Fabbro, J.L. Faure, F. Ferri, S. Ganjour,
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J. Rander, A. Rosowsky, I. Shreyber, M. Titov
DSM/IRFU, CEA/Saclay, Gif-sur-Yvette, France
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Laboratoire Leprince-Ringuet, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France
J.-L. Agram 14 , J. Andrea, D. Bloch, D. Bodin, J.-M. Brom, M. Cardaci, E.C. Chabert, C. Collard, E. Conte 14 ,
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Institut Pluridisciplinaire Hubert Curien, Université de Strasbourg, Université de Haute Alsace Mulhouse, CNRS/IN2P3, Strasbourg, France
318
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F. Fassi, D. Mercier
Centre de Calcul de l’Institut National de Physique Nucleaire et de Physique des Particules, CNRS/IN2P3, Villeurbanne, France
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L. Sgandurra, V. Sordini, Y. Tschudi, P. Verdier, S. Viret
Université de Lyon, Université Claude Bernard Lyon 1, CNRS-IN2P3, Institut de Physique Nucléaire de Lyon, Villeurbanne, France
Z. Tsamalaidze 15
Institute of High Energy Physics and Informatization, Tbilisi State University, Tbilisi, Georgia
G. Anagnostou, C. Autermann, S. Beranek, M. Edelhoff, L. Feld, N. Heracleous, O. Hindrichs, R. Jussen,
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B. Wittmer, V. Zhukov 16
RWTH Aachen University, I. Physikalisches Institut, Aachen, Germany
M. Ata, J. Caudron, E. Dietz-Laursonn, D. Duchardt, M. Erdmann, R. Fischer, A. Güth, T. Hebbeker,
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RWTH Aachen University, III. Physikalisches Institut A, Aachen, Germany
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RWTH Aachen University, III. Physikalisches Institut B, Aachen, Germany
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Deutsches Elektronen-Synchrotron, Hamburg, Germany
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G. Kaussen, H. Kirschenmann, R. Klanner, J. Lange, B. Mura, F. Nowak, T. Peiffer, N. Pietsch, D. Rathjens,
C. Sander, H. Schettler, P. Schleper, E. Schlieckau, A. Schmidt, M. Schröder, T. Schum, M. Seidel, V. Sola,
H. Stadie, G. Steinbrück, J. Thomsen, L. Vanelderen
University of Hamburg, Hamburg, Germany
C. Barth, J. Berger, C. Böser, T. Chwalek, W. De Boer, A. Descroix, A. Dierlamm, M. Feindt, M. Guthoff 5 ,
C. Hackstein, F. Hartmann, T. Hauth 5 , M. Heinrich, H. Held, K.H. Hoffmann, U. Husemann, I. Katkov 16 ,
J.R. Komaragiri, P. Lobelle Pardo, D. Martschei, S. Mueller, Th. Müller, M. Niegel, A. Nürnberg, O. Oberst,
A. Oehler, J. Ott, G. Quast, K. Rabbertz, F. Ratnikov, N. Ratnikova, S. Röcker, F.-P. Schilling, G. Schott,
H.J. Simonis, F.M. Stober, D. Troendle, R. Ulrich, J. Wagner-Kuhr, S. Wayand, T. Weiler, M. Zeise
Institut für Experimentelle Kernphysik, Karlsruhe, Germany
G. Daskalakis, T. Geralis, S. Kesisoglou, A. Kyriakis, D. Loukas, I. Manolakos, A. Markou, C. Markou,
C. Mavrommatis, E. Ntomari
Institute of Nuclear Physics “Demokritos”, Aghia Paraskevi, Greece
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L. Gouskos, T.J. Mertzimekis, A. Panagiotou, N. Saoulidou
University of Athens, Athens, Greece
I. Evangelou, C. Foudas, P. Kokkas, N. Manthos, I. Papadopoulos, V. Patras
University of Ioánnina, Ioánnina, Greece
G. Bencze, C. Hajdu, P. Hidas, D. Horvath 18 , F. Sikler, V. Veszpremi, G. Vesztergombi 19
KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary
N. Beni, S. Czellar, J. Molnar, J. Palinkas, Z. Szillasi
Institute of Nuclear Research ATOMKI, Debrecen, Hungary
J. Karancsi, P. Raics, Z.L. Trocsanyi, B. Ujvari
University of Debrecen, Debrecen, Hungary
S.B. Beri, V. Bhatnagar, N. Dhingra, R. Gupta, M. Kaur, M.Z. Mehta, N. Nishu, L.K. Saini, A. Sharma,
J.B. Singh
Panjab University, Chandigarh, India
Ashok Kumar, Arun Kumar, S. Ahuja, A. Bhardwaj, B.C. Choudhary, S. Malhotra, M. Naimuddin, K. Ranjan,
V. Sharma, R.K. Shivpuri
University of Delhi, Delhi, India
S. Banerjee, S. Bhattacharya, S. Dutta, B. Gomber, Sa. Jain, Sh. Jain, R. Khurana, S. Sarkar, M. Sharan
Saha Institute of Nuclear Physics, Kolkata, India
A. Abdulsalam, R.K. Choudhury, D. Dutta, S. Kailas, V. Kumar, P. Mehta, A.K. Mohanty 5 , L.M. Pant,
P. Shukla
Bhabha Atomic Research Centre, Mumbai, India
T. Aziz, S. Ganguly, M. Guchait 20 , M. Maity 21 , G. Majumder, K. Mazumdar, G.B. Mohanty, B. Parida,
K. Sudhakar, N. Wickramage
Tata Institute of Fundamental Research – EHEP, Mumbai, India
S. Banerjee, S. Dugad
Tata Institute of Fundamental Research – HECR, Mumbai, India
H. Arfaei 22 , H. Bakhshiansohi, S.M. Etesami 23 , A. Fahim 22 , M. Hashemi, H. Hesari, A. Jafari, M. Khakzad,
M. Mohammadi Najafabadi, S. Paktinat Mehdiabadi, B. Safarzadeh 24 , M. Zeinali
Institute for Research in Fundamental Sciences (IPM), Tehran, Iran
M. Abbrescia a,b , L. Barbone a,b , C. Calabria a,b,5 , S.S. Chhibra a,b , A. Colaleo a , D. Creanza a,c ,
N. De Filippis a,c,5 , M. De Palma a,b , L. Fiore a , G. Iaselli a,c , L. Lusito a,b , G. Maggi a,c , M. Maggi a ,
B. Marangelli a,b , S. My a,c , S. Nuzzo a,b , N. Pacifico a,b , A. Pompili a,b , G. Pugliese a,c , G. Selvaggi a,b ,
L. Silvestris a , G. Singh a,b , R. Venditti a,b , G. Zito a
a
b
c
INFN Sezione di Bari, Bari, Italy
Università di Bari, Bari, Italy
Politecnico di Bari, Bari, Italy
G. Abbiendi a , A.C. Benvenuti a , D. Bonacorsi a,b , S. Braibant-Giacomelli a,b , L. Brigliadori a,b ,
P. Capiluppi a,b , A. Castro a,b , F.R. Cavallo a , M. Cuffiani a,b , G.M. Dallavalle a , F. Fabbri a , A. Fanfani a,b ,
D. Fasanella a,b,5 , P. Giacomelli a , C. Grandi a , L. Guiducci a,b , S. Marcellini a , G. Masetti a ,
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M. Meneghelli a,b,5 , A. Montanari a , F.L. Navarria a,b , F. Odorici a , A. Perrotta a , F. Primavera a,b ,
A.M. Rossi a,b , T. Rovelli a,b , G.P. Siroli a,b , R. Travaglini a,b
a
b
INFN Sezione di Bologna, Bologna, Italy
Università di Bologna, Bologna, Italy
S. Albergo a,b , G. Cappello a,b , M. Chiorboli a,b , S. Costa a,b , R. Potenza a,b , A. Tricomi a,b , C. Tuve a,b
a
b
INFN Sezione di Catania, Catania, Italy
Università di Catania, Catania, Italy
G. Barbagli a , V. Ciulli a,b , C. Civinini a , R. D’Alessandro a,b , E. Focardi a,b , S. Frosali a,b , E. Gallo a ,
S. Gonzi a,b , M. Meschini a , S. Paoletti a , G. Sguazzoni a , A. Tropiano a
a
b
INFN Sezione di Firenze, Firenze, Italy
Università di Firenze, Firenze, Italy
L. Benussi, S. Bianco, S. Colafranceschi 25 , F. Fabbri, D. Piccolo
INFN Laboratori Nazionali di Frascati, Frascati, Italy
P. Fabbricatore a , R. Musenich a , S. Tosi a,b
a
b
INFN Sezione di Genova, Genova, Italy
Università di Genova, Genova, Italy
A. Benaglia a,b , F. De Guio a,b , L. Di Matteo a,b,5 , S. Fiorendi a,b , S. Gennai a,5 , A. Ghezzi a,b , S. Malvezzi a ,
R.A. Manzoni a,b , A. Martelli a,b , A. Massironi a,b,5 , D. Menasce a , L. Moroni a , M. Paganoni a,b , D. Pedrini a ,
S. Ragazzi a,b , N. Redaelli a , S. Sala a , T. Tabarelli de Fatis a,b
a
b
INFN Sezione di Milano-Bicocca, Milano, Italy
Università di Milano-Bicocca, Milano, Italy
S. Buontempo a , C.A. Carrillo Montoya a , N. Cavallo a,26 , A. De Cosa a,b,5 , O. Dogangun a,b , F. Fabozzi a,26 ,
A.O.M. Iorio a , L. Lista a , S. Meola a,27 , M. Merola a,b , P. Paolucci a,5
a
b
INFN Sezione di Napoli, Napoli, Italy
Università di Napoli “Federico II”, Napoli, Italy
P. Azzi a , N. Bacchetta a,5 , D. Bisello a,b , A. Branca a,b,5 , R. Carlin a,b , P. Checchia a , T. Dorigo a , U. Dosselli a ,
F. Gasparini a,b , U. Gasparini a,b , A. Gozzelino a , K. Kanishchev a,c , S. Lacaprara a , I. Lazzizzera a,c ,
M. Margoni a,b , A.T. Meneguzzo a,b , J. Pazzini a,b , N. Pozzobon a,b , P. Ronchese a,b , F. Simonetto a,b ,
E. Torassa a , M. Tosi a,b,5 , S. Vanini a,b , P. Zotto a,b , G. Zumerle a,b
a
b
c
INFN Sezione di Padova, Padova, Italy
Università di Padova, Padova, Italy
Università di Trento (Trento), Padova, Italy
M. Gabusi a,b , S.P. Ratti a,b , C. Riccardi a,b , P. Torre a,b , P. Vitulo a,b
a
b
INFN Sezione di Pavia, Pavia, Italy
Università di Pavia, Pavia, Italy
M. Biasini a,b , G.M. Bilei a , L. Fanò a,b , P. Lariccia a,b , G. Mantovani a,b , M. Menichelli a , A. Nappi a,b,† ,
F. Romeo a,b , A. Saha a , A. Santocchia a,b , A. Spiezia a,b , S. Taroni a,b
a
b
INFN Sezione di Perugia, Perugia, Italy
Università di Perugia, Perugia, Italy
P. Azzurri a,c , G. Bagliesi a , J. Bernardini a , T. Boccali a , G. Broccolo a,c , R. Castaldi a , R.T. D’Agnolo a,c,5 ,
R. Dell’Orso a , F. Fiori a,b,5 , L. Foà a,c , A. Giassi a , A. Kraan a , F. Ligabue a,c , T. Lomtadze a , L. Martini a,28 ,
A. Messineo a,b , F. Palla a , A. Rizzi a,b , A.T. Serban a,29 , P. Spagnolo a , P. Squillacioti a,5 , R. Tenchini a ,
G. Tonelli a,b , A. Venturi a , P.G. Verdini a
a
b
c
INFN Sezione di Pisa, Pisa, Italy
Università di Pisa, Pisa, Italy
Scuola Normale Superiore di Pisa, Pisa, Italy
CMS Collaboration / Physics Letters B 720 (2013) 309–329
L. Barone a,b , F. Cavallari a , D. Del Re a,b , M. Diemoz a , C. Fanelli a,b , M. Grassi a,b,5 , E. Longo a,b ,
P. Meridiani a,5 , F. Micheli a,b , S. Nourbakhsh a,b , G. Organtini a,b , R. Paramatti a , S. Rahatlou a,b ,
M. Sigamani a , L. Soffi a,b
a
b
INFN Sezione di Roma, Roma, Italy
Università di Roma, Roma, Italy
N.
N.
N.
A.
a
b
c
Amapane a,b , R. Arcidiacono a,c , S. Argiro a,b , M. Arneodo a,c , C. Biino a , N. Cartiglia a , M. Costa a,b ,
Demaria a , C. Mariotti a,5 , S. Maselli a , E. Migliore a,b , V. Monaco a,b , M. Musich a,5 , M.M. Obertino a,c ,
Pastrone a , M. Pelliccioni a , A. Potenza a,b , A. Romero a,b , R. Sacchi a,b , A. Solano a,b , A. Staiano a ,
Vilela Pereira a , L. Visca a,b
INFN Sezione di Torino, Torino, Italy
Università di Torino, Torino, Italy
Università del Piemonte Orientale (Novara), Torino, Italy
S. Belforte a , V. Candelise a,b , M. Casarsa a , F. Cossutti a , G. Della Ricca a,b , B. Gobbo a , M. Marone a,b,5 ,
D. Montanino a,b,5 , A. Penzo a , A. Schizzi a,b
a
b
INFN Sezione di Trieste, Trieste, Italy
Università di Trieste, Trieste, Italy
S.G. Heo, T.Y. Kim, S.K. Nam
Kangwon National University, Chunchon, Republic of Korea
S. Chang, D.H. Kim, G.N. Kim, D.J. Kong, H. Park, S.R. Ro, D.C. Son, T. Son
Kyungpook National University, Daegu, Republic of Korea
J.Y. Kim, Zero J. Kim, S. Song
Chonnam National University, Institute for Universe and Elementary Particles, Kwangju, Republic of Korea
S. Choi, D. Gyun, B. Hong, M. Jo, H. Kim, T.J. Kim, K.S. Lee, D.H. Moon, S.K. Park
Korea University, Seoul, Republic of Korea
M. Choi, J.H. Kim, C. Park, I.C. Park, S. Park, G. Ryu
University of Seoul, Seoul, Republic of Korea
Y. Cho, Y. Choi, Y.K. Choi, J. Goh, M.S. Kim, E. Kwon, B. Lee, J. Lee, S. Lee, H. Seo, I. Yu
Sungkyunkwan University, Suwon, Republic of Korea
M.J. Bilinskas, I. Grigelionis, M. Janulis, A. Juodagalvis
Vilnius University, Vilnius, Lithuania
H. Castilla-Valdez, E. De La Cruz-Burelo, I. Heredia-de La Cruz, R. Lopez-Fernandez, R. Magaña Villalba,
J. Martínez-Ortega, A. Sánchez-Hernández, L.M. Villasenor-Cendejas
Centro de Investigacion y de Estudios Avanzados del IPN, Mexico City, Mexico
S. Carrillo Moreno, F. Vazquez Valencia
Universidad Iberoamericana, Mexico City, Mexico
H.A. Salazar Ibarguen
Benemerita Universidad Autonoma de Puebla, Puebla, Mexico
E. Casimiro Linares, A. Morelos Pineda, M.A. Reyes-Santos
Universidad Autónoma de San Luis Potosí, San Luis Potosí, Mexico
321
322
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D. Krofcheck
University of Auckland, Auckland, New Zealand
A.J. Bell, P.H. Butler, R. Doesburg, S. Reucroft, H. Silverwood
University of Canterbury, Christchurch, New Zealand
M. Ahmad, M.H. Ansari, M.I. Asghar, H.R. Hoorani, S. Khalid, W.A. Khan, T. Khurshid, S. Qazi, M.A. Shah,
M. Shoaib
National Centre for Physics, Quaid-I-Azam University, Islamabad, Pakistan
H. Bialkowska, B. Boimska, T. Frueboes, R. Gokieli, M. Górski, M. Kazana, K. Nawrocki,
K. Romanowska-Rybinska, M. Szleper, G. Wrochna, P. Zalewski
National Centre for Nuclear Research, Swierk, Poland
G. Brona, K. Bunkowski, M. Cwiok, W. Dominik, K. Doroba, A. Kalinowski, M. Konecki, J. Krolikowski
Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland
N. Almeida, P. Bargassa, A. David, P. Faccioli, P.G. Ferreira Parracho, M. Gallinaro, J. Seixas, J. Varela,
P. Vischia
Laboratório de Instrumentação e Física Experimental de Partículas, Lisboa, Portugal
I. Belotelov, I. Golutvin, I. Gorbunov, A. Kamenev, V. Karjavin, V. Konoplyanikov, G. Kozlov, A. Lanev,
A. Malakhov, P. Moisenz, V. Palichik, V. Perelygin, M. Savina, S. Shmatov, V. Smirnov, A. Volodko,
A. Zarubin
Joint Institute for Nuclear Research, Dubna, Russia
S. Evstyukhin, V. Golovtsov, Y. Ivanov, V. Kim, P. Levchenko, V. Murzin, V. Oreshkin, I. Smirnov,
V. Sulimov, L. Uvarov, S. Vavilov, A. Vorobyev, An. Vorobyev
Petersburg Nuclear Physics Institute, Gatchina (St. Petersburg), Russia
Yu. Andreev, A. Dermenev, S. Gninenko, N. Golubev, M. Kirsanov, N. Krasnikov, V. Matveev,
A. Pashenkov, D. Tlisov, A. Toropin
Institute for Nuclear Research, Moscow, Russia
V. Epshteyn, M. Erofeeva, V. Gavrilov, M. Kossov, N. Lychkovskaya, V. Popov, G. Safronov, S. Semenov,
V. Stolin, E. Vlasov, A. Zhokin
Institute for Theoretical and Experimental Physics, Moscow, Russia
A. Belyaev, E. Boos, M. Dubinin 4 , L. Dudko, A. Ershov, A. Gribushin, V. Klyukhin, O. Kodolova, I. Lokhtin,
A. Markina, S. Obraztsov, M. Perfilov, S. Petrushanko, A. Popov, L. Sarycheva † , V. Savrin, A. Snigirev
Moscow State University, Moscow, Russia
V. Andreev, M. Azarkin, I. Dremin, M. Kirakosyan, A. Leonidov, G. Mesyats, S.V. Rusakov, A. Vinogradov
P.N. Lebedev Physical Institute, Moscow, Russia
I. Azhgirey, I. Bayshev, S. Bitioukov, V. Grishin 5 , V. Kachanov, D. Konstantinov, V. Krychkine, V. Petrov,
R. Ryutin, A. Sobol, L. Tourtchanovitch, S. Troshin, N. Tyurin, A. Uzunian, A. Volkov
State Research Center of Russian Federation, Institute for High Energy Physics, Protvino, Russia
P. Adzic 30 , M. Djordjevic, M. Ekmedzic, D. Krpic 30 , J. Milosevic
University of Belgrade, Faculty of Physics and Vinca Institute of Nuclear Sciences, Belgrade, Serbia
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M. Aguilar-Benitez, J. Alcaraz Maestre, P. Arce, C. Battilana, E. Calvo, M. Cerrada, M. Chamizo Llatas,
N. Colino, B. De La Cruz, A. Delgado Peris, D. Domínguez Vázquez, C. Fernandez Bedoya,
J.P. Fernández Ramos, A. Ferrando, J. Flix, M.C. Fouz, P. Garcia-Abia, O. Gonzalez Lopez, S. Goy Lopez,
J.M. Hernandez, M.I. Josa, G. Merino, J. Puerta Pelayo, A. Quintario Olmeda, I. Redondo, L. Romero,
J. Santaolalla, M.S. Soares, C. Willmott
Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain
C. Albajar, G. Codispoti, J.F. de Trocóniz
Universidad Autónoma de Madrid, Madrid, Spain
H. Brun, J. Cuevas, J. Fernandez Menendez, S. Folgueras, I. Gonzalez Caballero, L. Lloret Iglesias,
J. Piedra Gomez
Universidad de Oviedo, Oviedo, Spain
J.A. Brochero Cifuentes, I.J. Cabrillo, A. Calderon, S.H. Chuang, J. Duarte Campderros, M. Felcini 31 ,
M. Fernandez, G. Gomez, J. Gonzalez Sanchez, A. Graziano, C. Jorda, A. Lopez Virto, J. Marco, R. Marco,
C. Martinez Rivero, F. Matorras, F.J. Munoz Sanchez, T. Rodrigo, A.Y. Rodríguez-Marrero, A. Ruiz-Jimeno,
L. Scodellaro, I. Vila, R. Vilar Cortabitarte
Instituto de Física de Cantabria (IFCA), CSIC-Universidad de Cantabria, Santander, Spain
D. Abbaneo, E. Auffray, G. Auzinger, M. Bachtis, P. Baillon, A.H. Ball, D. Barney, J.F. Benitez, C. Bernet 6 ,
G. Bianchi, P. Bloch, A. Bocci, A. Bonato, C. Botta, H. Breuker, T. Camporesi, G. Cerminara, T. Christiansen,
J.A. Coarasa Perez, D. D’Enterria, A. Dabrowski, A. De Roeck, S. Di Guida, M. Dobson, N. Dupont-Sagorin,
A. Elliott-Peisert, B. Frisch, W. Funk, G. Georgiou, M. Giffels, D. Gigi, K. Gill, D. Giordano, M. Girone,
M. Giunta, F. Glege, R. Gomez-Reino Garrido, P. Govoni, S. Gowdy, R. Guida, M. Hansen, P. Harris,
C. Hartl, J. Harvey, B. Hegner, A. Hinzmann, V. Innocente, P. Janot, K. Kaadze, E. Karavakis, K. Kousouris,
P. Lecoq, Y.-J. Lee, P. Lenzi, C. Lourenço, N. Magini, T. Mäki, M. Malberti, L. Malgeri, M. Mannelli,
L. Masetti, F. Meijers, S. Mersi, E. Meschi, R. Moser, M.U. Mozer, M. Mulders, P. Musella, E. Nesvold,
T. Orimoto, L. Orsini, E. Palencia Cortezon, E. Perez, L. Perrozzi, A. Petrilli, A. Pfeiffer, M. Pierini, M. Pimiä,
D. Piparo, G. Polese, L. Quertenmont, A. Racz, W. Reece, J. Rodrigues Antunes, G. Rolandi 32 , C. Rovelli 33 ,
M. Rovere, H. Sakulin, F. Santanastasio, C. Schäfer, C. Schwick, I. Segoni, S. Sekmen, A. Sharma, P. Siegrist,
P. Silva, M. Simon, P. Sphicas 34 , D. Spiga, A. Tsirou, G.I. Veres 19 , J.R. Vlimant, H.K. Wöhri, S.D. Worm 35 ,
W.D. Zeuner
CERN, European Organization for Nuclear Research, Geneva, Switzerland
W. Bertl, K. Deiters, W. Erdmann, K. Gabathuler, R. Horisberger, Q. Ingram, H.C. Kaestli, S. König,
D. Kotlinski, U. Langenegger, F. Meier, D. Renker, T. Rohe, J. Sibille 36
Paul Scherrer Institut, Villigen, Switzerland
L. Bäni, P. Bortignon, M.A. Buchmann, B. Casal, N. Chanon, A. Deisher, G. Dissertori, M. Dittmar,
M. Donegà, M. Dünser, J. Eugster, K. Freudenreich, C. Grab, D. Hits, P. Lecomte, W. Lustermann,
A.C. Marini, P. Martinez Ruiz del Arbol, N. Mohr, F. Moortgat, C. Nägeli 37 , P. Nef, F. Nessi-Tedaldi,
F. Pandolfi, L. Pape, F. Pauss, M. Peruzzi, F.J. Ronga, M. Rossini, L. Sala, A.K. Sanchez, A. Starodumov 38 ,
B. Stieger, M. Takahashi, L. Tauscher † , A. Thea, K. Theofilatos, D. Treille, C. Urscheler, R. Wallny,
H.A. Weber, L. Wehrli
Institute for Particle Physics, ETH Zurich, Zurich, Switzerland
C. Amsler, V. Chiochia, S. De Visscher, C. Favaro, M. Ivova Rikova, B. Millan Mejias, P. Otiougova,
P. Robmann, H. Snoek, S. Tupputi, M. Verzetti
Universität Zürich, Zurich, Switzerland
324
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S. Bahinipati, Y.H. Chang, K.H. Chen, C.M. Kuo, S.W. Li, W. Lin, Z.K. Liu, Y.J. Lu, D. Mekterovic, A.P. Singh,
R. Volpe, S.S. Yu
National Central University, Chung-Li, Taiwan
P. Bartalini, P. Chang, Y.H. Chang, Y.W. Chang, Y. Chao, K.F. Chen, C. Dietz, U. Grundler, W.-S. Hou,
Y. Hsiung, K.Y. Kao, Y.J. Lei, R.-S. Lu, D. Majumder, E. Petrakou, X. Shi, J.G. Shiu, Y.M. Tzeng, X. Wan,
M. Wang
National Taiwan University (NTU), Taipei, Taiwan
B. Asavapibhop, N. Srimanobhas
Chulalongkorn University, Bangkok, Thailand
A. Adiguzel, M.N. Bakirci 39 , S. Cerci 40 , C. Dozen, I. Dumanoglu, E. Eskut, S. Girgis, G. Gokbulut,
E. Gurpinar, I. Hos, E.E. Kangal, T. Karaman, G. Karapinar 41 , A. Kayis Topaksu, G. Onengut, K. Ozdemir,
S. Ozturk 42 , A. Polatoz, K. Sogut 43 , D. Sunar Cerci 40 , B. Tali 40 , H. Topakli 39 , L.N. Vergili, M. Vergili
Cukurova University, Adana, Turkey
I.V. Akin, T. Aliev, B. Bilin, S. Bilmis, M. Deniz, H. Gamsizkan, A.M. Guler, K. Ocalan, A. Ozpineci, M. Serin,
R. Sever, U.E. Surat, M. Yalvac, E. Yildirim, M. Zeyrek
Middle East Technical University, Physics Department, Ankara, Turkey
E. Gülmez, B. Isildak 44 , M. Kaya 45 , O. Kaya 45 , S. Ozkorucuklu 46 , N. Sonmez 47
Bogazici University, Istanbul, Turkey
K. Cankocak
Istanbul Technical University, Istanbul, Turkey
L. Levchuk
National Scientific Center, Kharkov Institute of Physics and Technology, Kharkov, Ukraine
F. Bostock, J.J. Brooke, E. Clement, D. Cussans, H. Flacher, R. Frazier, J. Goldstein, M. Grimes, G.P. Heath,
H.F. Heath, L. Kreczko, S. Metson, D.M. Newbold 35 , K. Nirunpong, A. Poll, S. Senkin, V.J. Smith,
T. Williams
University of Bristol, Bristol, United Kingdom
L. Basso 48 , K.W. Bell, A. Belyaev 48 , C. Brew, R.M. Brown, D.J.A. Cockerill, J.A. Coughlan, K. Harder,
S. Harper, J. Jackson, B.W. Kennedy, E. Olaiya, D. Petyt, B.C. Radburn-Smith,
C.H. Shepherd-Themistocleous, I.R. Tomalin, W.J. Womersley
Rutherford Appleton Laboratory, Didcot, United Kingdom
R. Bainbridge, G. Ball, R. Beuselinck, O. Buchmuller, D. Colling, N. Cripps, M. Cutajar, P. Dauncey,
G. Davies, M. Della Negra, W. Ferguson, J. Fulcher, D. Futyan, A. Gilbert, A. Guneratne Bryer, G. Hall,
Z. Hatherell, J. Hays, G. Iles, M. Jarvis, G. Karapostoli, L. Lyons, A.-M. Magnan, J. Marrouche, B. Mathias,
R. Nandi, J. Nash, A. Nikitenko 38 , A. Papageorgiou, J. Pela, M. Pesaresi, K. Petridis, M. Pioppi 49 ,
D.M. Raymond, S. Rogerson, A. Rose, M.J. Ryan, C. Seez, P. Sharp † , A. Sparrow, M. Stoye, A. Tapper,
M. Vazquez Acosta, T. Virdee, S. Wakefield, N. Wardle, T. Whyntie
Imperial College, London, United Kingdom
M. Chadwick, J.E. Cole, P.R. Hobson, A. Khan, P. Kyberd, D. Leggat, D. Leslie, W. Martin, I.D. Reid,
P. Symonds, L. Teodorescu, M. Turner
Brunel University, Uxbridge, United Kingdom
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K. Hatakeyama, H. Liu, T. Scarborough
Baylor University, Waco, USA
O. Charaf, C. Henderson, P. Rumerio
The University of Alabama, Tuscaloosa, USA
A. Avetisyan, T. Bose, C. Fantasia, A. Heister, J. St. John, P. Lawson, D. Lazic, J. Rohlf, D. Sperka, L. Sulak
Boston University, Boston, USA
J. Alimena, S. Bhattacharya, D. Cutts, A. Ferapontov, U. Heintz, S. Jabeen, G. Kukartsev, E. Laird,
G. Landsberg, M. Luk, M. Narain, D. Nguyen, M. Segala, T. Sinthuprasith, T. Speer, K.V. Tsang
Brown University, Providence, USA
R. Breedon, G. Breto, M. Calderon De La Barca Sanchez, S. Chauhan, M. Chertok, J. Conway, R. Conway,
P.T. Cox, J. Dolen, R. Erbacher, M. Gardner, R. Houtz, W. Ko, A. Kopecky, R. Lander, O. Mall, T. Miceli,
D. Pellett, F. Ricci-tam, B. Rutherford, M. Searle, J. Smith, M. Squires, M. Tripathi, R. Vasquez Sierra
University of California, Davis, Davis, USA
V. Andreev, D. Cline, R. Cousins, J. Duris, S. Erhan, P. Everaerts, C. Farrell, J. Hauser, M. Ignatenko,
C. Jarvis, C. Plager, G. Rakness, P. Schlein † , P. Traczyk, V. Valuev, M. Weber
University of California, Los Angeles, Los Angeles, USA
J. Babb, R. Clare, M.E. Dinardo, J. Ellison, J.W. Gary, F. Giordano, G. Hanson, G.Y. Jeng 50 , H. Liu, O.R. Long,
A. Luthra, H. Nguyen, S. Paramesvaran, J. Sturdy, S. Sumowidagdo, R. Wilken, S. Wimpenny
University of California, Riverside, Riverside, USA
W. Andrews, J.G. Branson, G.B. Cerati, S. Cittolin, D. Evans, F. Golf, A. Holzner, R. Kelley, M. Lebourgeois,
J. Letts, I. Macneill, B. Mangano, S. Padhi, C. Palmer, G. Petrucciani, M. Pieri, M. Sani, V. Sharma,
S. Simon, E. Sudano, M. Tadel, Y. Tu, A. Vartak, S. Wasserbaech 51 , F. Würthwein, A. Yagil, J. Yoo
University of California, San Diego, La Jolla, USA
D. Barge, R. Bellan, C. Campagnari, M. D’Alfonso, T. Danielson, K. Flowers, P. Geffert, J. Incandela,
C. Justus, P. Kalavase, S.A. Koay, D. Kovalskyi, V. Krutelyov, S. Lowette, N. Mccoll, V. Pavlunin, F. Rebassoo,
J. Ribnik, J. Richman, R. Rossin, D. Stuart, W. To, C. West
University of California, Santa Barbara, Santa Barbara, USA
A. Apresyan, A. Bornheim, Y. Chen, E. Di Marco, J. Duarte, M. Gataullin, Y. Ma, A. Mott, H.B. Newman,
C. Rogan, M. Spiropulu, V. Timciuc, J. Veverka, R. Wilkinson, S. Xie, Y. Yang, R.Y. Zhu
California Institute of Technology, Pasadena, USA
B. Akgun, V. Azzolini, A. Calamba, R. Carroll, T. Ferguson, Y. Iiyama, D.W. Jang, Y.F. Liu, M. Paulini,
H. Vogel, I. Vorobiev
Carnegie Mellon University, Pittsburgh, USA
J.P. Cumalat, B.R. Drell, W.T. Ford, A. Gaz, E. Luiggi Lopez, J.G. Smith, K. Stenson, K.A. Ulmer, S.R. Wagner
University of Colorado at Boulder, Boulder, USA
J. Alexander, A. Chatterjee, N. Eggert, L.K. Gibbons, B. Heltsley, A. Khukhunaishvili, B. Kreis, N. Mirman,
G. Nicolas Kaufman, J.R. Patterson, A. Ryd, E. Salvati, W. Sun, W.D. Teo, J. Thom, J. Thompson, J. Tucker,
J. Vaughan, Y. Weng, L. Winstrom, P. Wittich
Cornell University, Ithaca, USA
326
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D. Winn
Fairfield University, Fairfield, USA
S. Abdullin, M. Albrow, J. Anderson, L.A.T. Bauerdick, A. Beretvas, J. Berryhill, P.C. Bhat, I. Bloch,
K. Burkett, J.N. Butler, V. Chetluru, H.W.K. Cheung, F. Chlebana, V.D. Elvira, I. Fisk, J. Freeman, Y. Gao,
D. Green, O. Gutsche, J. Hanlon, R.M. Harris, J. Hirschauer, B. Hooberman, S. Jindariani, M. Johnson,
U. Joshi, B. Kilminster, B. Klima, S. Kunori, S. Kwan, C. Leonidopoulos, J. Linacre, D. Lincoln, R. Lipton,
J. Lykken, K. Maeshima, J.M. Marraffino, S. Maruyama, D. Mason, P. McBride, K. Mishra, S. Mrenna,
Y. Musienko 52 , C. Newman-Holmes, V. O’Dell, O. Prokofyev, E. Sexton-Kennedy, S. Sharma, W.J. Spalding,
L. Spiegel, L. Taylor, S. Tkaczyk, N.V. Tran, L. Uplegger, E.W. Vaandering, R. Vidal, J. Whitmore, W. Wu,
F. Yang, F. Yumiceva, J.C. Yun
Fermi National Accelerator Laboratory, Batavia, USA
D. Acosta, P. Avery, D. Bourilkov, M. Chen, T. Cheng, S. Das, M. De Gruttola, G.P. Di Giovanni, D. Dobur,
A. Drozdetskiy, R.D. Field, M. Fisher, Y. Fu, I.K. Furic, J. Gartner, J. Hugon, B. Kim, J. Konigsberg,
A. Korytov, A. Kropivnitskaya, T. Kypreos, J.F. Low, K. Matchev, P. Milenovic 53 , G. Mitselmakher, L. Muniz,
M. Park, R. Remington, A. Rinkevicius, P. Sellers, N. Skhirtladze, M. Snowball, J. Yelton, M. Zakaria
University of Florida, Gainesville, USA
V. Gaultney, S. Hewamanage, L.M. Lebolo, S. Linn, P. Markowitz, G. Martinez, J.L. Rodriguez
Florida International University, Miami, USA
T. Adams, A. Askew, J. Bochenek, J. Chen, B. Diamond, S.V. Gleyzer, J. Haas, S. Hagopian, V. Hagopian,
M. Jenkins, K.F. Johnson, H. Prosper, V. Veeraraghavan, M. Weinberg
Florida State University, Tallahassee, USA
M.M. Baarmand, B. Dorney, M. Hohlmann, H. Kalakhety, I. Vodopiyanov
Florida Institute of Technology, Melbourne, USA
M.R. Adams, I.M. Anghel, L. Apanasevich, Y. Bai, V.E. Bazterra, R.R. Betts, I. Bucinskaite, J. Callner,
R. Cavanaugh, O. Evdokimov, L. Gauthier, C.E. Gerber, D.J. Hofman, S. Khalatyan, F. Lacroix, M. Malek,
C. O’Brien, C. Silkworth, D. Strom, P. Turner, N. Varelas
University of Illinois at Chicago (UIC), Chicago, USA
U. Akgun, E.A. Albayrak, B. Bilki 54 , W. Clarida, F. Duru, S. Griffiths, J.-P. Merlo, H. Mermerkaya 55 ,
A. Mestvirishvili, A. Moeller, J. Nachtman, C.R. Newsom, E. Norbeck, Y. Onel, F. Ozok 56 , S. Sen, P. Tan,
E. Tiras, J. Wetzel, T. Yetkin, K. Yi
The University of Iowa, Iowa City, USA
B.A. Barnett, B. Blumenfeld, S. Bolognesi, D. Fehling, G. Giurgiu, A.V. Gritsan, Z.J. Guo, G. Hu,
P. Maksimovic, S. Rappoccio, M. Swartz, A. Whitbeck
Johns Hopkins University, Baltimore, USA
P. Baringer, A. Bean, G. Benelli, R.P. Kenny Iii, M. Murray, D. Noonan, S. Sanders, R. Stringer, G. Tinti,
J.S. Wood, V. Zhukova
The University of Kansas, Lawrence, USA
A.F. Barfuss, T. Bolton, I. Chakaberia, A. Ivanov, S. Khalil, M. Makouski, Y. Maravin, S. Shrestha,
I. Svintradze
Kansas State University, Manhattan, USA
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J. Gronberg, D. Lange, D. Wright
Lawrence Livermore National Laboratory, Livermore, USA
A. Baden, M. Boutemeur, B. Calvert, S.C. Eno, J.A. Gomez, N.J. Hadley, R.G. Kellogg, M. Kirn, T. Kolberg,
Y. Lu, M. Marionneau, A.C. Mignerey, K. Pedro, A. Peterman, A. Skuja, J. Temple, M.B. Tonjes, S.C. Tonwar,
E. Twedt
University of Maryland, College Park, USA
A. Apyan, G. Bauer, J. Bendavid, W. Busza, E. Butz, I.A. Cali, M. Chan, V. Dutta, G. Gomez Ceballos,
M. Goncharov, K.A. Hahn, Y. Kim, M. Klute, K. Krajczar 57 , P.D. Luckey, T. Ma, S. Nahn, C. Paus, D. Ralph,
C. Roland, G. Roland, M. Rudolph, G.S.F. Stephans, F. Stöckli, K. Sumorok, K. Sung, D. Velicanu,
E.A. Wenger, R. Wolf, B. Wyslouch, M. Yang, Y. Yilmaz, A.S. Yoon, M. Zanetti
Massachusetts Institute of Technology, Cambridge, USA
S.I. Cooper, B. Dahmes, A. De Benedetti, G. Franzoni, A. Gude, S.C. Kao, K. Klapoetke, Y. Kubota, J. Mans,
N. Pastika, R. Rusack, M. Sasseville, A. Singovsky, N. Tambe, J. Turkewitz
University of Minnesota, Minneapolis, USA
L.M. Cremaldi, R. Kroeger, L. Perera, R. Rahmat, D.A. Sanders
University of Mississippi, Oxford, USA
E. Avdeeva, K. Bloom, S. Bose, J. Butt, D.R. Claes, A. Dominguez, M. Eads, J. Keller, I. Kravchenko,
J. Lazo-Flores, H. Malbouisson, S. Malik, G.R. Snow
University of Nebraska-Lincoln, Lincoln, USA
U. Baur, A. Godshalk, I. Iashvili, S. Jain, A. Kharchilava, A. Kumar, S.P. Shipkowski, K. Smith
State University of New York at Buffalo, Buffalo, USA
G. Alverson ∗ , E. Barberis, D. Baumgartel, M. Chasco, J. Haley, D. Nash, D. Trocino, D. Wood, J. Zhang
Northeastern University, Boston, USA
A. Anastassov, A. Kubik, N. Mucia, N. Odell, R.A. Ofierzynski, B. Pollack, A. Pozdnyakov, M. Schmitt,
S. Stoynev, M. Velasco, S. Won
Northwestern University, Evanston, USA
L. Antonelli, D. Berry, A. Brinkerhoff, K.M. Chan, M. Hildreth, C. Jessop, D.J. Karmgard, J. Kolb, K. Lannon,
W. Luo, S. Lynch, N. Marinelli, D.M. Morse, T. Pearson, M. Planer, R. Ruchti, J. Slaunwhite, N. Valls,
M. Wayne, M. Wolf
University of Notre Dame, Notre Dame, USA
B. Bylsma, L.S. Durkin, C. Hill, R. Hughes, K. Kotov, T.Y. Ling, D. Puigh, M. Rodenburg, C. Vuosalo,
G. Williams, B.L. Winer
The Ohio State University, Columbus, USA
N. Adam, E. Berry, P. Elmer, D. Gerbaudo, V. Halyo, P. Hebda, J. Hegeman, A. Hunt, P. Jindal,
D. Lopes Pegna, P. Lujan, D. Marlow, T. Medvedeva, M. Mooney, J. Olsen, P. Piroué, X. Quan, A. Raval,
B. Safdi, H. Saka, D. Stickland, C. Tully, J.S. Werner, A. Zuranski
Princeton University, Princeton, USA
E. Brownson, A. Lopez, H. Mendez, J.E. Ramirez Vargas
University of Puerto Rico, Mayaguez, USA
328
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E. Alagoz, V.E. Barnes, D. Benedetti, G. Bolla, D. Bortoletto, M. De Mattia, A. Everett, Z. Hu, M. Jones,
O. Koybasi, M. Kress, A.T. Laasanen, N. Leonardo, V. Maroussov, P. Merkel, D.H. Miller, N. Neumeister,
I. Shipsey, D. Silvers, A. Svyatkovskiy, M. Vidal Marono, H.D. Yoo, J. Zablocki, Y. Zheng
Purdue University, West Lafayette, USA
S. Guragain, N. Parashar
Purdue University Calumet, Hammond, USA
A. Adair, C. Boulahouache, K.M. Ecklund, F.J.M. Geurts, W. Li, B.P. Padley, R. Redjimi, J. Roberts, J. Zabel
Rice University, Houston, USA
B. Betchart, A. Bodek, Y.S. Chung, R. Covarelli, P. de Barbaro, R. Demina, Y. Eshaq, T. Ferbel,
A. Garcia-Bellido, P. Goldenzweig, J. Han, A. Harel, D.C. Miner, D. Vishnevskiy, M. Zielinski
University of Rochester, Rochester, USA
A. Bhatti, R. Ciesielski, L. Demortier, K. Goulianos, G. Lungu, S. Malik, C. Mesropian
The Rockefeller University, New York, USA
S. Arora, A. Barker, J.P. Chou, C. Contreras-Campana, E. Contreras-Campana, D. Duggan, D. Ferencek,
Y. Gershtein, R. Gray, E. Halkiadakis, D. Hidas, A. Lath, S. Panwalkar, M. Park, R. Patel, V. Rekovic,
J. Robles, K. Rose, S. Salur, S. Schnetzer, C. Seitz, S. Somalwar, R. Stone, S. Thomas
Rutgers, the State University of New Jersey, Piscataway, USA
G. Cerizza, M. Hollingsworth, S. Spanier, Z.C. Yang, A. York
University of Tennessee, Knoxville, USA
R. Eusebi, W. Flanagan, J. Gilmore, T. Kamon 58 , V. Khotilovich, R. Montalvo, I. Osipenkov, Y. Pakhotin,
A. Perloff, J. Roe, A. Safonov, T. Sakuma, S. Sengupta, I. Suarez, A. Tatarinov, D. Toback
Texas A&M University, College Station, USA
N. Akchurin, J. Damgov, C. Dragoiu, P.R. Dudero, C. Jeong, K. Kovitanggoon, S.W. Lee, T. Libeiro, Y. Roh,
I. Volobouev
Texas Tech University, Lubbock, USA
E. Appelt, A.G. Delannoy, C. Florez, S. Greene, A. Gurrola, W. Johns, C. Johnston, P. Kurt, C. Maguire,
A. Melo, M. Sharma, P. Sheldon, B. Snook, S. Tuo, J. Velkovska
Vanderbilt University, Nashville, USA
M.W. Arenton, M. Balazs, S. Boutle, B. Cox, B. Francis, J. Goodell, R. Hirosky, A. Ledovskoy, C. Lin, C. Neu,
J. Wood, R. Yohay
University of Virginia, Charlottesville, USA
S. Gollapinni, R. Harr, P.E. Karchin, C. Kottachchi Kankanamge Don, P. Lamichhane, A. Sakharov
Wayne State University, Detroit, USA
M. Anderson, D. Belknap, L. Borrello, D. Carlsmith, M. Cepeda, S. Dasu, E. Friis, L. Gray, K.S. Grogg,
M. Grothe, R. Hall-Wilton, M. Herndon, A. Hervé, P. Klabbers, J. Klukas, A. Lanaro, C. Lazaridis, J. Leonard,
R. Loveless, A. Mohapatra, I. Ojalvo, F. Palmonari, G.A. Pierro, I. Ross, A. Savin, W.H. Smith, J. Swanson
University of Wisconsin, Madison, USA
CMS Collaboration / Physics Letters B 720 (2013) 309–329
*
Corresponding author.
†
Deceased.
1
Also at Vienna University of Technology, Vienna, Austria.
2
Also at National Institute of Chemical Physics and Biophysics, Tallinn, Estonia.
3
Also at Universidade Federal do ABC, Santo Andre, Brazil.
4
Also at California Institute of Technology, Pasadena, USA.
5
Also at CERN, European Organization for Nuclear Research, Geneva, Switzerland.
6
Also at Laboratoire Leprince-Ringuet, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France.
7
Also at Suez Canal University, Suez, Egypt.
8
Also at Zewail City of Science and Technology, Zewail, Egypt.
9
Also at Cairo University, Cairo, Egypt.
10
Also at Fayoum University, El-Fayoum, Egypt.
11
Also at British University, Cairo, Egypt.
12
Now at Ain Shams University, Cairo, Egypt.
13
Also at National Centre for Nuclear Research, Swierk, Poland.
14
Also at Université de Haute-Alsace, Mulhouse, France.
15
Now at Joint Institute for Nuclear Research, Dubna, Russia.
16
Also at Moscow State University, Moscow, Russia.
17
Also at Brandenburg University of Technology, Cottbus, Germany.
18
Also at Institute of Nuclear Research ATOMKI, Debrecen, Hungary.
19
Also at Eötvös Loránd University, Budapest, Hungary.
20
Also at Tata Institute of Fundamental Research – HECR, Mumbai, India.
21
Also at University of Visva-Bharati, Santiniketan, India.
22
Also at Sharif University of Technology, Tehran, Iran.
23
Also at Isfahan University of Technology, Isfahan, Iran.
24
Also at Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran, Iran.
25
Also at Facoltà Ingegneria Università di Roma, Roma, Italy.
26
Also at Università della Basilicata, Potenza, Italy.
27
Also at Università degli Studi Guglielmo Marconi, Roma, Italy.
28
Also at Università degli Studi di Siena, Siena, Italy.
29
Also at University of Bucharest, Faculty of Physics, Bucuresti-Magurele, Romania.
30
Also at Faculty of Physics of University of Belgrade, Belgrade, Serbia.
31
Also at University of California, Los Angeles, Los Angeles, USA.
32
Also at Scuola Normale e Sezione dell’INFN, Pisa, Italy.
33
Also at INFN Sezione di Roma; Università di Roma, Roma, Italy.
34
Also at University of Athens, Athens, Greece.
35
Also at Rutherford Appleton Laboratory, Didcot, United Kingdom.
36
Also at The University of Kansas, Lawrence, USA.
37
Also at Paul Scherrer Institut, Villigen, Switzerland.
38
Also at Institute for Theoretical and Experimental Physics, Moscow, Russia.
39
Also at Gaziosmanpasa University, Tokat, Turkey.
40
Also at Adiyaman University, Adiyaman, Turkey.
41
Also at Izmir Institute of Technology, Izmir, Turkey.
42
Also at The University of Iowa, Iowa City, USA.
43
Also at Mersin University, Mersin, Turkey.
44
Also at Ozyegin University, Istanbul, Turkey.
45
Also at Kafkas University, Kars, Turkey.
46
Also at Suleyman Demirel University, Isparta, Turkey.
47
Also at Ege University, Izmir, Turkey.
48
Also at School of Physics and Astronomy, University of Southampton, Southampton, United Kingdom.
49
Also at INFN Sezione di Perugia; Università di Perugia, Perugia, Italy.
50
Also at University of Sydney, Sydney, Australia.
51
Also at Utah Valley University, Orem, USA.
52
Also at Institute for Nuclear Research, Moscow, Russia.
53
Also at University of Belgrade, Faculty of Physics and Vinca Institute of Nuclear Sciences, Belgrade, Serbia.
54
Also at Argonne National Laboratory, Argonne, USA.
55
Also at Erzincan University, Erzincan, Turkey.
56
Also at Mimar Sinan University, Istanbul, Istanbul, Turkey.
57
Also at KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary.
58
Also at Kyungpook National University, Daegu, Republic of Korea.
329